1. Field of the Invention
The invention relates generally to detection, identification, and classification of metallic objects, and more particularly, to a system and method for efficient installation of ferromagnetic loops on traveling surfaces.
2. Background of the Invention
Applicants reference U.S. patent application Ser. No. 10/953,858, filed Sep. 30, 2004 (“the '858 application”), which is a continuation of U.S. patent application Ser. No. 10/206,972, (the '972 application, now U.S. Pat. No. 6,864,804), which is a continuation-in-part application of U.S. patent application Ser. No. 10/098,131, filed Mar. 15, 2002 (“the '131 application”), which is a continuation-in-part application of U.S. patent application Ser. No. 09/977,937 (“the '937 application”), filed Oct. 17, 2001 (now U.S. Pat. No. 7,136,828). All of the above patents and patent applications are hereby incorporated herein by reference in their entirety.
The presence or passage of vehicles on roadways or other information regarding vehicles on roadways can be monitored with a combination of loop detectors, treadles, or other such devices capable of detecting passing vehicles. These devices may be used to detect vehicles in toll collection stations, stoplights, or in other applications. These devices may provide vehicle classification information as vehicles pass along a roadway.
One example of the use of such devices is a toll collection system such as, for example, that described in the '972 application referenced above. The '972 application relates to an intelligent vehicle identification system (IVIS) that includes one or more inductive loops. The inductive loops disclosed in the '972 application includes signature loops, wheel assembly loops, intelligent queue loops, wheel axle loops, gate loops, vehicle separation loops, and enforcement loops.
Key elements of the ferromagnetic loops disclosed in the '972 application include the magnetic strength of the flux field, height and length. The flux field created by the loop circuit is concentrated and low to the road surface to maximize the ferromagnetic effect of the wheel assemblies and minimize the eddy currents created by vehicle chassis. Shallow installation of a wire used to form loop sensors, such as ferromagnetic loop sensors, may be important for optimal performance of the ferromagnetic loop design.
Since loop sensors, such as ferromagnetic loop sensors, are arranged in the bed of a roadway, permanent installation of the sensors typically entails cutting into the roadbed to provide a space to house the loop sensors. Referring now to FIGS. 12, 13, and 14 (which correspond to FIGS. 31b, 41 and 50 from the '972 application, respectively), the roadbed may be cut in a predetermined pattern according to the desired shape of the loop sensor, such as the pattern shown in FIG. 14. FIG. 14 illustrates loop sensors 5010, 5020, and 5030 connected to loop detector 5002. A narrow groove is cut to house the wire, as illustrated in FIG. 12, where wire 3118 is housed in a groove 3130 of pavement 3102. One method of installation involves installing the wire within one inch of the road surface as shown in FIG. 13. Groove depth 4108 in FIG. 13 is in the range of one inch. Wire turns 4102 and 4104 can be accommodated within a groove.
The above installation method requires cuts to be made into a web of grooves (also termed “groove web” hereinafter) in the shape of the loop sensor. In addition, after grooves are cut, it is necessary to lay a continuous sensor wire in a serpentine manner within the groove web to form the desired sensor shape. It may also be necessary to secure the continuous wire within the web of grooves, for example, using a bonding agent. In addition, the step of laying the continuous sensor wire can involve laying two or more turns in the groove pattern, as illustrated in FIG. 13. The above procedure can entail considerable time and difficulty, causing a travel lane to be inoperable for a considerable time. In addition, control of position of the sensor within a groove web can be difficult. For example, as indicated in FIG. 12, a groove width must be somewhat larger than a sensor wire diameter, leaving room for the sensor wire to shift within the groove during laying of the wire. In particular, as described in the '972 application, in order to control the induction loop properties, it is important to control the depth of the sensor wires with respect to a surface in which they are embedded. Inadvertent variations in the sensor loop wire depth incurred in the above process during wire laying, can cause unwanted changes in the loop properties. Additionally, variation in loop properties from sensor to sensor can be expected for induction loop sensors fabricated with nominally the same pattern, groove depth, and wire arrangement.
In light of the foregoing, it will be appreciated that a need exists to improve loop sensor installation.